The Inhibition Mechanism Research Of Thioacetamide Compounds On Cyanobacteria

Currently,cyanobacteria bloom frequently brings great threat to human life an d attracts more and more attention.In the previous work of our group,we used t he important regulatory enzyme in the Calvin cycle,fructose-1,6-diphosphate/stemo heptulose-1,7-bisphosphatase(Cy-FBP/SBPase)as the target obtained thioacetamide compounds with good inhibitiory activity,named TAD-Ⅰ,TAD-Ⅲ,TAD-Ⅳ.The value of EC50 of these compounds in 200 μL culture system of Synechocysis sp.P CC 6803 were 0.46μM,0.08μM and 0.13μM.In this paper,the culture system w as expanded to 100 mL.Effects of our compounds thioacetamide analogs on cell,chlorophyll a content,physiochemical and antioxidant responses of Synechocysis sp.PCC 6803 and Microcystis aeruginosa were compared.The main results are as follows:a)The Inhibition mechanism of TAD-Ⅰ on cyanobacteriaWhen the initial concentration of Synechocysis sp.PCC 6803 and Microcystis aeruginosa 905 were OD730=0.02 ± 0.005,compared with the control CuSO4,TAD-Ⅰshowed similar inhibitory acticity on the growth of the two cyanobacterial strains.Further studies showed that TAD-Ⅰ inhibited activity of the photosynthetic system of two cyanobacteria more strongly than CuSO4.0.5-2μM TAD-I has little influence on the antioxidant system of the two kinds of algae.When the final concentration of TAD-Ⅰroused to ≥ 3 μM,the oxidative damage of PCC6803 was increased.Meanwhile,the effect of TAD-I on the growth and photosynthesis system of Cy-FBP/SBPase overexpressing mutant cyanobacteria PSB in PCC 6803 was further studied,the results showed that the activity of TAD-I on PSB was lower than that of PCC 6803.It is speculated that TAD-I bound to Cy-FBP/SBPase which caused the decrease of photosynthesis.When the initial concentration of Synechocysis sp.PCC 6803 and Microcystis aeruginosa 905 were OD730=0.32±0.02,TAD-Ⅰ has a slow growth inhibitory effect of the two cyanobacterial strains.b)The Inhibition mechanism of TAD-Ⅲ on cyanobacteriaWhen the initial concentration of Synechocysis sp.PCC 6803 and Microcystis aeruginosa 905 were OD730=0.02±0.005,compared with CuSO4,TAD-Ⅲ showed a stronger inhibitory effect on the growth of the two cyanobacterial strains,and the inhibitory effect of TAD-Ⅲ on the growth of Microcystis aeruginosa 905 was about 10 times of that on Synechocysis sp.PCC 6803.Further studies found that TAD-Ⅲ had stronger inhibitory activity on PS Ⅱ of two cyanobacteria than CuSO4.At the same time,TAD-Ⅲ had less oxidative damage to Synechocysis sp.PCC 6803,but had greater oxidative damage to Microcystis aeruginosa 905.Further studies showed that TAD-Ⅲcould lead to the release of the intracellular algae toxin,and the increase of content of extracellular algae toxin.it is speculated that TAD-Ⅲ has an influence on the integrity of cell membrane.When the initial concentration of Synechocysis sp.PCC 6803 and Microcystis aeruginosa 905 were OD730=0.32 ± 0.02,TAD-Ⅲ has a slow growth inhibitory effect of the two cyanobacterial strains.c)The Inhibition mechanism of TAD-Ⅳ on cyanobacteriaWhen the initial concentration of Synechocysis sp.PCC 6803 and Microcystis aeruginosa 905 were OD730=0.02 ± 0.005,compared with CuSO4,TAD-Ⅳ showed a strong inhibitory effect on the growth of the two cyanobacterial strains.Further studies showed that TAD-Ⅳ has greater influence on the activity of photosynthetic system than CuSO4.The results of oxidative stress indicated that TAD-Ⅳ would aggravate the lipid peroxidation reaction of Synechocysis sp.PCC 6803.It is speculated that TAD-Ⅳinhibited the growth of cyanobacteria by inhibiting photosynthesis and antioxidant system.When the initial concentration of Synechocysis sp.PCC 6803 and Microcystis aeruginosa 905 were OD730=0.32±0.02,TAD-Ⅳ has a slow growth inhibitory effect of the two cyanobacterial strains.To sum up,it is speculated that TAD-Ⅰ affected the activity of photosynthesis by inhibiting the activity of Cy-FBP/SBPase in cyanobacteria and caused the accumulation of oxidized free radicals.TAD-Ⅲ and TAD-Ⅳ inhibited the photosynthesis system and antioxidant system.Meanwhile,TAD-Ⅲ could increase the permeability of the plasma membrane and decrease total microcystin cencentration.